Grohedal cistern leaks?
I followed the helpful suggestions and solved the problem in minutes by piercing the pimpled washers.
Wonderful input as I was on the verge of buying a new complete cistern. Low marks to Grohe however for having a defective product out there and no helpful admission to purchasers.Upgraded replacement neoprene washers would only cost them pennies.
Peter Stevenson Perth, July 2014